This invention relates to a direct-current motor, and more specifically to a direct-current motor which is particularly--but not exclusively--suited for driving compressors in refrigeration systems or aggregates.
Direct-current motors are often desired to be used because of their advantageous torque and their start-up characteristics. A particular application where such motors would be desirable is for driving compressors of refrigeration aggregates for mobile applications, such as in vehicles, boats or the like. Such vehicles and similar devices usually have a direct-current power supply from which the motor could be powered. However, when direct-current motors are used in such applications it is necessary in many instances to take relatively cumbersome and expensive steps to provide protection against disadvantageous influences resulting from spark formation between the brushes and the collector of the motor commutator. For example, if such a motor is used for driving a compressor of a refrigeration aggregate, the formation of sparks may lead to a deterioration of the cooling medium and to the formation of highly aggressive substances which can attack and cause damge to the entire system.
Nevertheless, the advantages of direct-current motors for the types of applications mentioned above are so significant that it has been proposed to provide for torque-transfer by means of contact-less couplings with a separator between the coupling sections, one of which is driven by the armature of the motor and the other of which is driven by the coupling and in turn drives the device to be powered, e.g. the refrigeration compressor, so that the component of the system which requires protection against sparking is separated from the source of the sparking. However, experience has shown that this construction is very expensive, and, moreover, is capable of transmitting only a relatively low torque which does not meet all requirements.